Vibratable platen means in selective printing machines



United States Patent [72] inventors William H. Plumpe;

Theodore E. Weischelbaum, St. Louis, Mo. [21] Appl. No. 702,581

[22] Filed Feb. 2, 1968 [-45] Patented Dec. 15,1970

[73] Assignee Sherwood Medical Industries Chicago, Ill. a corporation of Delaware. by mesne assignment [54] VIBRATABLE'PLATEN MEANS IN SELECTIVE [56] I References Cited UNITED STATES PATENTS 923,085 5/1909 Smith 101/90 1,489,500 4/1924 Lord..... 197/36 1,935,194 11/1933 Wilsey 101/297X Primary Examiner-William B. Penn Attorney-Hofgren, Wegner, Allen, Stellman & McCord ABSTRACT: A mechanism for printing indicia on paper webs or strips characterized in that the impression member comprises an indicia bearing wheel wherein the indicium preferably follow the periphery of the wheel and the striking member comprises a harmonically vibratable reed preferably excited by an electromagnet.

Also, a means for orienting a rotationally displaceable member, such as a printing wheel, fixed to a shaft comprising a toothed wheel on the shaft and an electromagnet adjacent the wheel having spaced core ends of a width preferably equal to the width of the space between the teeth of the wheel.

Further, a lost motion connection for driving a rotationally displaceable member, such as a potentiometer, comprising a driving disc having an arcuate slot, a driven disc also having an arcuate slot, and an intermediate disc having oppositely projecting pins normally held against a corresponding edge of each slot by spring means.

PATENTED nan 5 19in SHEET 2 OF 4 1. VIBRATABLE PLATEN MEANSIN SELECTIVE PRINTING MACHINES BACKGROUND OF THE IN \(ENTION 1. Field of the Invention This invention relates to an improvement in printer away from the print member to transfer indicia to a web or sheet fed between the two-indicia or characters may be formed in relative relief on one of the impression or movable striking members. Typically, the impression member is in roll or plate form and the striking member may also be in roll form or generally in the form of a hammer. In either system an imprint is obtained on the paper web or sheet as a result of engagement between the impression and striking members.

Recently there has been developed achemically treated paper which produces an image matching the configuration of a memberpressed against the paper. One example of such a paper is that manufactured by Minnesota Mining and Manufacturing Corporation and sold under the name Action Paper. It has been found that in printing on paper such SUMMARY OF THE INVENTION This invention is directed, in brief, to an improved printing mechanism of the type having a temporarily fixed impression Preferably, to absorb shock, a lost motion connection means is coupled between a rotationally displaceable member,

. such as the shaft of a potentiometer, and a driving member,

such-as the rotational output of a servomechanism. The lost motion connection comprises three disks connected by pin and'slot arrangements with spring means normally urging the pin to a rest position relative to the slot. Sudden rotational torque, such as caused by one of the members coming to an abrupt stop, is initially absorbed until a pin is rotated into engagement with the edge of a slot. When the torque is terminated, the pin is returned to the rest position.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a printer mechanism embodying this invention;

FIG. 2 is an enlarged top plan view of the interior of the printer shown in FIG. 1 illustrating the elements of this invention in greater detail;

FIG. 3 is a front elevational view of the structure shown in FIG. 2;

FIG. 4 is a fragmentary enlarged section view taken generally along the line 4-4 of FIG. 3;

FIG. 5 is a fragmentary section view taken generally along the. line 5-5 of FIG. 3;

FIG. 6 is.a fragmentary sectional view taken generally along the line 6-6 of FIG. 3; I

FIG. 7 is a fragmentary section view taken generally along the line 7-7 of FIG. 3;

FIG. 8 is an exploded view of the lost motion system of the servo drive train for the printer of this invention; and

FIGS. 9A through 9.! are a sequential illustration of one cycle ofa printing operation of the printer of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 1 with windows 16a and 16b and a slot 18 through which paper member and a striking member movable toward and away y from the impression member with printing indicia or characters carried by one of the members, wherein the movable member is constructed and arranged to rapidly engage the fixed member repeatedly for printing single indicium, and during such repeated engagement different areas of the indicium are brought into engagement with a sheet to which its image is to be transferred. I

The best mode currently contemplated for carrying out this invention comprises a printing mechanism wherein at least one impression member'is a print wheel provided with radially upstanding indicia or characters and the movable striking I member comprises a harmonically vibratable reed overlying each movable print wheel. An electromagnet is positioned adjacent the reed so that activation of the magnet excites the reed and causes it to go through a series of undulations, during which the free end of the reed repeatedly engages one of the upstanding indicium on the print wheel in different areas of the indicium as the reed harmonically vibrates. Preferably, paper having the characteristics of the previously referred to Action Paper" type is interposed between the reed and the print wheel so that at the completion of the cycle the image of the indicium on the print wheel is produced in the paper.

To orient at least one print wheel in a proper printing posi .20 extends. This invention is not limited to use with a printer utilizing paper of web or sheet form, but in the illustrated embodiment paper is shown in web form, fed from a roll 20a which is rotatably mounted on a shaft 20b in the interior of housing 12.

Framing members in the interior of the housing include a base 22 with uprights 24a through 23c. Depending framing members 26 extend downwardly from the underside of cover 14 and are connected thereto by suitable fastening means 28. In addition, the framing members 26 are also pivoted to uprights 24b and 24d at 30 so that as the cover is swung between an open and closed position as shown in FIG. 4, the members 26 pivot with respect to the uprights 24b and 24d.

Mounted to the depending framing members 26 is the movable striking means 32 and the means 34 for activating the movable striking means 32. in particular, the movable striking means preferably comprises thin elongated reeds 36 extending from a thin base 36a, and formed from a metallic material such as steel. Base 36a is connected to a cross bar 38 which spans the distance between the frame members 26.

Means 34 preferably is an electromagnet 40 having a generally U-shaped core 42, of soft iron or other magnetizable material, terminating in space ends or pole pieces 42a and 42b, and a coil of wire 44. Electromagnet 40 is of the well known type which, upon energization of coil 44 by a suitable source of electric potential, causes a magnetic field to be induced in core 42 and through the air gap between pole pieces 42a and 4211, which field attracts the metallic reeds 36 and cause vibration thereof, as will be explained in greater detail later.

Positioned below the downturned free ends 36b of the reeds 36 are impression forming means in the forms of indicia bearing wheels 46 which are mounted on shafts 48 and 49 and have radially outstanding indicium 50 protruding outwardly from the periphery thereof in a generally circular outline. In operation, with paper 20 webbed between the reeds 36 and the periphery of wheels 46, energization of electromagnet 40 will cause a harmonic vibration in reeds 36 so that the reeds press the paper against the indicium 50 as they undulate through a cycle as illustrated in FIGS. 9A through J, to be explained in greater detail later. 1

In the illustrated embodiment the wheels 46 are mounted in two sets of two groups, one group constituting a step by step reference or index number group and the other group constituting a variable numerical value group. One set in each group is intended for viewing through Windows 160 and 16b and the other set in each group is located adjacent the free ends of the reeds 36 and is intended for printing on web 20. Thus, at any one given time, the variable numerical value being printed can be visually read through window 16a and the number representing the order in-the printing sequence at which the variable numerical value is being printed can be read through window 16b. Depending upon the location of the windows 16a and 16b, it might be necessary for the indicia wheels 46 which are positioned for viewing through windows 16a and 16b to be offset with respect to the indicia wheels which are intended for performing the printing function. The wheels 46 include interconnected gearing means of the well known types, such as utilized in speedometers or the like, so that incremental advances of the rightmost wheel causes one incremental advance of the next wheel, and 100 incremental advances of the rightmost wheel causes 10 incremental advances of the next left adjacent wheel and one incremental advance of the second left adjacent indicia wheel, and so on. This type of interrelationship between indicia wheels is old and well known in the art and thus will not be described further in detail herein. For the sake of simplicity, the two sets of three wheels will be referred to as index number wheels, and the two sets of four wheels will be referred to as variable value wheels. Those wheels which are visible through the windows 16a and 16b will be referred to as the reading wheels, and those sets which are adjacent the free ends of the reeds 36 will be referred to as the printing wheels.

The index number wheel sets are mounted on shaft 49 which is journaled for rotation in uprights 24a, b and 0. Adjacent upright 24a, shaft 49 bears a pawl or gear 52. A small tooth 53 pivotally depends from an arm 54 that generally overhangs pawl 52. Arm 54 in turn, is pivoted at 55 to a frame member on the exterior of coil 56. As coil 56 is energized, the arm 54 is pulled downwardly and fdrwardly so that the tooth 53 engages the pawl 52 and rotates the shaft 49 through one incremental advance. Coil 56 is electrically connected to circuitry (not illustrated) for operating the other components of the printer so that after each variable number value is printed, coil 56 is energized to cause the arm 54 and tooth 53 to advance shaft 49 one increment so that the index number wheels will read and print the next sequential number in the series of variable values that are being registered by the printer.

Shaft 48, which drives the variable value reading and printing wheels, is journaled for rotation at uprights 24c, 24d and 24e. Shaft 48 extends through a bearing in upright 24c and is directly coupled to the output armature shaft 58 of a motor 59, which drives shaft 48 and the variable numerical value wheels mounted thereon, as will appear. Adjacent upright 24c, the shaft 48 has a small gear 61. This gear is in engagement with large gear 62 which, by means of the lost motion system 63, best illustrated in FIG. 8 and to be described in detail later, drives the shaft 64 of a wire wound potentiometer 65. Motor 59 and potentiometer 65 may be connected in a conventional servomechanism circuit to convert an electrical input signal representative of a numerical value into a corresponding amount of rotational motion of shaft 48. For this purpose, the output leads 66 of potentiometer 65 may be connected in a feedback circuit (not illustrated) to produce a voltage output which equals the value of the electrical input signal which caused motor 59 to drive potentiometer 65 to its instant position. Desirably, the voltage from potentiometer 65 cancels the input voltage to the servomechanism, producing a zero volt signal to motor 59 when the system is at null. When the servomechanism comes to rest, the output shaft 58 of motor 59 has been rotated by a predetermined amount in either a clockwise or counterclockwise direction. This, in turn, rotates the shaft 48 and causes displacement of the indicia wheels 46 of the variable value reading and printing sets so that the wheels of the sets are displaced to represent a value through the viewing window 16a and in printing relationship with respect to the reeds 36, which value is related to the voltages supplied to the servomechanism.

Motor 59 may take any suitable form useable in a servomechanism circuit. Purely by way of example, motor 59 may be a shaded pole motor having separate shading coils 67 and 67". one of the shading coils 67 is shorted, the armature output shaft 58 of the motor turns in one direction, whereas when the opposite shading coil is shorted, the armature turns in the opposite direction. A conventional circuit may be used to short the appropriate shading coil 67, thereby driving the armature in the proper rotational direction, when the servomechanism is off null. Similarly, conventional means may be used to brake the armature of motor 59 as the servomechanism approaches null, and to open the previously shorted shading coil when the system reaches null.

Means are also provided for positively orienting or detenting the variable value integer wheels so that they will be properly oriented with respect to the printing station and the window 16a following the advancement of the wheels by the motor 59. That is, for purposes of printing an integer number, the units or right-hand wheel is magnetically detented to the nearest whole number should the motor 59 drive the printing wheels to some position which is fractionally between two integers. In the illustrated embodiment this means takes the form of an electromagnet 68 having a generally U-shaped magnetizable core 70, seen best in FIG. 6, which terminates in free ends or poles 70a and 70b to concentrate the magnetic field, and a coil 72. Electromagnet 68 is positioned closely adjacent a magnetizable toothed wheel 74 of soft iron or similar material which is mounted on shaft 48 near upright 2411, to which coil 68 is connected by bracket 76. While wheel 74 is illustrated as being located in the same plane as the poles 70, such construction is in no way necessary, and the planes of wheel 74 and poles 70 could be displaced if desirable. Furthermore, a portion of the teeth of wheel 74 could overlap, i.e., be located alongside, the poles 70. The several radially outwardly projecting teeth 78 of wheel 74 are preferably of the same width as the free ends 70a and 70b of coil 76, and the space between adjacent teeth 78 is preferably equal to the width of the free ends 70a and 70b. Both teeth 78 and free ends 70a and 70b are preferably of flattopped construction, in order to form sharper discontinuous corners at which the magnetic field will concentrate.

After motor 59 has completed driving shaft 48 to a particular position, the electromagnet 68 is energized to induce a magnetic field between ends 700' and 7012. As the field seeks the path of least reluctance, the teeth 78 of wheel 74 will move into alignment directly adjacent the ends 70a and 70b, thereby causing some displacement in wheel 74 which, in turn, will slightly displace shaft 48 and thereby properly align or orient the integer wheel of the variable value reading and printing sets with respect to both the viewing window and the reeds 36.

Because the width of teeth 78 is preferably equal to the width of the air gap between the adjacent teeth, the magnetic field will always cause the closest tooth to move into alignment with the free ends 70a and 70b. Furthermore, because the pole and space are between teeth of the same size, the dead zone of the wheel is narrowed, since such structure gives the maximum percentage change in flux path for a given angular movement. With this structure, only the exact center or bridging position represents a point at which the magnetic forces tending to cause rotation in both directions are equal.

. tooth 78 nearest the free ends 70a and 70b.

Means are also provided for incrementally advancing the paper from the roll 20a to place the paper in position to receive another set of numbers to be printed thereupon, following each movement of the variable value wheels to a new position responsive to activation of motor 59'and each movement of the index number wheels responsive to activation of coil 56. Included in this means is a paper drive motor 80 having a drive shaft 82, on which is fixed a gear 84; Gear 84 drives chain 86 which is' also wrapped about sprocket or gear 88 fixed on a shaft 92. g

A sleeve 90 is fixedly secured for rotation with shaft 92 which is fixed in uprights 24b and 24d. Web 20 is fed from roll 200 up and over wheels 46, and downwardly under sleeve 90. Rotation of sleeve 90 responsive to driving of shaft 92 by gear 88 will advance web 20 relative to wheels 46 of the printing station.

Means are provided for terminating the actuation of paper drive motor 80 following a predetermined incrementaladvance of the web 20. In the illustrated embodiment, this means includes a paper drive motor switch 94, best seen in FIGS. 6 and 7, having an arm 96 which engages the teeth of ratchet wheel 98 mounted on shaft 92. As the shaft '92 is rotated by the chain 86 driving gear 88, the teeth of ratchet wheel 98 lift switch arm 96. This opens switch 94 which is in circuit with motor 80 to shut off the motor, thereby terminating the driving of the paper drive sleeve 90. Each lifting of the arm 96 terminates energization of the motor 80 so that the amount of incremental advance of the paper 20 by thesleeve 90 could be changed by changing the spacing between the teeth of ratchet wheel 98. To again energize motor 80, any conventional circuit (not illustrated) coupled in parallel with switch 94, may momentarily close to jumper switch 94, thereby momentarily energizing motor 80. The resulting incremental advance of shaft 92 drives arm 96 off the tooth of ratchet wheel 98 on which it was previously. resting. As arm96 is released, switch 94'closes to complete the motor energizing circuit. Motor 80 then remains actuated until the next tooth on ratchet wheel 98 again opens switch 94. I

Means are also provided for holding'the variable value printing wheels against relative rotational movement during the printing operation. Included in this means is an arm 100, FIG. 3, which is connected to a spring 102 fastened to a bracket 104 on base 22. Arm 100 isalso pivoted at 105 to a leg 106 of solenoid winding 107 so that spring 102 normally urges the arm 100 tothe left as seen in FIG. 3. Solenoid 107 has an iron core 108 adjacent arm 100'. When solenoid 107 is energized, core 108 concentrates the field and pulls arm 100 toward it and against the variable value print set of wheels and thereby urges the four print wheels 46 of the variable value print wheel group together. The frictional engagement afforded by pushing the wheels towards each other firmly secures the wheels against relative rotational movement. When the servomechanism including motor 59 receives a signal to drive shaft 48 and thereby change the positioning of the several variable value wheels 46, solenoid 107 is deactivated, an arm 100 releases its clamping action against the variable value print{set to permit rotation of .the wheels to a new position. 3

Lost motion connection 63 is provided in the drive train for potentiometer 65 to absorb the high impact torque which results when the internal wiper (not illustrated) in potentiometer 65 is driven against either its low or high stop or end tab. Without connection 63, the momentum of the driving system may shear off the stops when the wiper is driven to an extreme end position. By using connection 63, it is possible to use potentiometers having stops which could not withstand the impact force otherwise occurring. It is essential that potentiometer 65 and the variable numerical value wheels 64 at all times have the same or a corresponding rotational orientation with respect to each other, or the value printed will be in error. Lost motion connection 63 is designed both to absorb impact torque in either direction. and to always return after impact to the same rest position in order to maintain the correspondence between the position of shafts 48 and 64.

More particularly, sleeve 114, FIG. 8, is connected to potentiometer shaft 64 and extends through driving member or disc 116. Disc 116 is slotted transversely at 118. A generally U-shaped torsion spring 120, having a hooked end 120a, is connected to pin 121 of disc 116. Intermediate member or disc 122 facially abuts disc 116 and has a central opening 124 for loosely receiving sleeve 114. A pin 126 protrudes outwardly from both faces of disc 122, one end of which extends through opening 118 and engages hooked end 120a of torsion spring 120. Disc 122, in turn, facially abuts the gear 62 which has a central opening 128 for loosely receiving sleeve 114. Gear 62 also has a slot 130 positioned in transverse and radial alignment with slot 118 of disc 116 with respect to the axis of sleeve 114. A generally U-shaped torsion spring 132 having a hooked end 132a at slot 130, is connected to gear 62 by being hooked at its other end to pin 133.

The servomechanism, including motor 59, is not intended to be connected to an electrical input signal of such magnitude as to drive the wiper within the potentiometer beyond the position of the internal stops located therein. However, since it is practically impossible for the driving system to terminate its rotational output exactly at the end position of potentiometer 65, the wiper within potentiometer 65 may at times be driven against the stops located therein. Lost motion connection 63 is designed to absorb the resulting impact, and further to serve as a safety factor should an operator disregard the limits of the electrical signal input within which the printer is designed to operate. The internal stops of most potentiometers can withstand the full output torque of motor 59, once the wiper is resting against the stop. The purpose of the lost motion connection system is to safely absorb the initial impact as the wiper suddenly contacts a stop, so that the stop itself may thereafter safely hold the motor against further rotation.

In operation, as motor 59 is energized responsive to an input signal, gear 62 may be driven by gear 61 in either direction as viewed in FIGS. 6 and 7. As gear 62 and lost motion connection 63 turn sleeve 114 and connected shaft 64 in a counterclockwise direction for example, the internal wiper of potentiometer 65 may be driven against an internal stop, thereby suddenly restraining sleeve 114 from further counterclockwise rotation. The resulting impulse torque is first absorbed by the compression of spring 120. Should the servomechanism continue driving gear 62, pin 126 may abut edge 134 of slot 118, but with substantially reduced torque, allowing the internal stop of the potentiometer to safely absorb the impact momentum. Once the driving force of motor 59 is terminated, spring 120 will urge pin 126 against the opposite edge 136 of slot 118, so that it is returned to a rest position which always maintains the same corresponding position with reference to shaft 48, FIGS. 2 and 3.

Conversely, as motor 59 drives gear 62 in a clockwise direction, the internal wiper in potentiometer 65 may be driven against the opposite end stop. Pin 126 will now move against the action of torsion spring 132 in slot l30, causing the impulse torque to be absorbed. Should the motor continue to rotate gear 62, pin 126 may engage edge 137, however, the torque transmitted to the end stop of the potentiometer has been substantially reduced. When the driving action of motor 59 is terminated, spring 132 urges pin 126- back to its initial rest position, against edge 135 of slot 130. Thus, independent of whether the servomechanism is driving gear 62 in a clockwise direction or counterclockwise direction, means are provided for absorbing the impulse should the internal wiper in' the potentiometer be driven against a stop. Furthermore, the lost motion system thereafter automatically returns to a shaft position having the same relation to the printer wheels shaft position as existed prior to the stopping of the driven system.

While slots 118 and 130 are shown in alignment with each other an pin 126 is a unitary structurehaving a single axis parallel to that of sleeve 114, slots 118 and 130 could be radially and/or circumferentially offset, as well as the opposite ends ofpin 126. So long as the angular displacement necessary to engage the pin with the opposite edges of the slot remained generally the same, the lost motion connection afforded thereby would be the same as in the illustrated embodiment.

The general operation of the printer is as follows: An input signal is received by the servomechanism, and the resulting rotation of the armature 58 of motor 59 rotates the variable value wheel shaft 48. This rotates the far right, or integer wheel, of each of the four wheel reading and printing sets which, through the well known gear ratio interconnection with the remaining wheels of the sets rotates each of those remaining wheels after one, 10 and 100 full revolutions of the integer wheel. As the rotational movement of the wheels 46 is terminated, electromagnet 68 is energized, inducing a field between the free ends 70a and 70b of the core to align teeth 78 of wheel 74 with these free ends. This causes some slight rotational displacement of shaft 48 and insures proper registration of the integer wheel of the variable value printing set. Solenoid winding 107 is energized to pull arm 100 to the right and holds the variable value printing wheels in the selected position. Reeds 36 are then excited by electromagnet 40 and the index number and variable member is transferred to web 20.

After the numbers have been printed, paper drive motor 80 is energized by connecting power thereto, and, through the drive train of gear 84, chain 86 and gear 88, rotate shaft 92 and the connected paper feed sleeve 90 to advance strip or web of paper forwardly from roll 2011. After the paper advances to the next print position, the ratchet wheel 98 lifts the arm 96 which trips switch 94 and shuts off the power to paper drive motor 80.

Concurrently with the activation of servo motor 59 and paper drive motor 80, the coil 56 receives a signal which pulls arm 54 downwardly and forwardly so that the tooth 53 on the free end thereof engages the gear 52 on the index shaft 49 to advance that shaft through one increment of movement and, thereby advance the far right or integer wheel 46 of both the reading and printing set through one integer.

As previously explained, the reeds 36 are thin, elongated, metallic strips, with a slightly downtumed free end 36b which allows the reed to rock farther over the upraised curve indicium 50. Should the reeds be used with flat indicium, the curve at the end 36b should be reversed. That is, a slight upward curve is desired to preserve the rocking action. With indicium having a curve less than the curve of the printing wheel, it is possible to entirely eliminate the end curve of the reed, while still maintaining the same rocking action. The provision of the individual reeds for each print wheel substantially prevents interaction between the reeds to insure that each operates as a freely vibrating tongue like element. This prevents indicium 50 on an adjacent wheel, which may be slightly out of alignment with the instant wheel, from acting as a bridge which could otherwise prevent striking means 32 from striking all parts of the upraised indicium 50. It is to be understood that instead of vibrating the individual reeds, the base portion 36a could be vibrated to produce a similar action at the free end 36b of the reeds. If desired, a foam plastiemay be secured to the top of base portion 36a to deaden some of the noise from the vibrating reeds.

As seen in FIG. 98, as the electromagnet 44 is energized to induce a magnetic field which flows through core 42 and the air space between core ends 42a and 42b, the reed 36 is pulled downwardly. Since the portion of reed 36 nearest end 42b is less constrained than the portion near end 420, that portion will be urged downwardly the farthest distance, and preferably strikes end 42b, for reasons to be explained hereinafter. Terminating the energization of the electromagnet permits the reed 36 to lift and begin its harmonic oscillation, as shown in FIG. 9C. With reference to FIGS. 9D through I, it can be seen that the reed flexes between upwardly arching and downwardly bowed positions until returning to a position approximating the at rest position at FIG. 91. During all of this operation the curved end 36b repeatedly engages the adjacent indicium 50a of each print wheel 46, this engagement occurring in the form of a rocking action with respect to the indicium, more or less massaging the paper 20 in the area of the adjacent indicium 50 a. Thus, as the reed vibrates it engages different portions of the indicium 50a at different stages during the vibration. At any instant of time, the full force of the reed is exerted across a thin line contacting a small transverse section of the indicium, rather than being distributed across the whole indicium. The thin line of reed contact undulates across the whole indicium, resulting in a significantly greater force of metal impact than would otherwise be possible. This insures that the entire surface area of the indicium is urges against the web 20 in the zone immediately above the indicium with suffrcient pressure to provide good print transfer.

Preferably, the electromagnet 44 is energized a plurality of times for each intended print cycle, or, in other words, for each intended transfer of the image of indicium 500. By energizing the electromagnet 44 for several cycles, any spots skipped on the first stroke of reed 36 may be covered on the following strokes. In addition, reeds 36 are desirably chosen to have a natural frequency of vibration which complements or is generally in synchronism with the time period between each energization of the electromagnet. With such a construction, each energization of the electromagnet will reinforce the previous vibrations of the reed, causing high amplitude vibrations having maximum energy content.

For example, conventional 60 cycle AC line current may be rectified, and certain portions of the half wave AC (of which there are 60 half cycles per second) gated to the electromagnet. It has been found that passing six such half cycles to the electromagnet results in a satisfactory print transfer. That is, the cycle of operation shown in FIGS. 9Bthrough 9] is repeated six times for each cycle of print transfer. The entire six repetitions consumes a total amount of time on the order of OJ seconds. Each reed 36 is chosen to have a natural period of oscillation slightly lower than 60 cycles per second, in order that one complete cycle of vibration will occur during the half cycle that electromagnet 44 is not energized. During the period the reed is swinging free above the-paper, it acts as a reed having about a 55 cycles per second resonance with a high harmonic content. As the reed contacts the paper, it is operated in a higher mode. When the electromagnet is energized every 1/60 of a second, the reed automatically adjusts the length of time it is in each mode to give a total period of H60 ofa second. Because the reed is preferably tuned below the frequency of the electromagnet, it contacts the paper for a longer period of time. The natural resonance of the reed is primarily determined by its thickness and length, whereas its width is of minor importance and is merely chosen to be sufficient to cover the width of indicia 50.

For one specific embodiment, reeds 36 were formed from blue-tempered spring steel, and had the following dimensions. Each individual reed was 0.016 inches thick, and had a length of 1.5 inches from the downwardly turned free end 36b to the base portion 36a. Base 360 had a length of 2.0 inches from the beginning of the slotted individual reeds to the crossbar 38. The portion of base 36a clamped by crossbar 38 extended 0.75 inches. The width of each individual reed was 0.25 inches with a slightly increasing taper extending from end 36b toward base portion 36a. The natural resonance of the reed was approximately 55 cycles per second.

Whereas both portions of an AC current could be passed to the electromagnet, it is preferred that one one half cycle be gated to the electromagnet, in order that the reeds may vibrate freely, i.e., without being under the influence of a magnetic field, for a certain portion of time. Furthermore, while cycles per second will produce an operative system, it has been found that a system resonant at around one-half this frequency is preferred in that it is easier to attract the reeds and cause them to strike the electromagnet, regardless of their instantaneous position when the electromagnet was energized. This prevents the reedsfrom falling out of synchronism with the energization of the electromagnet should some external force unbalance the system.

Furthermore, each reed 36 desirably has a high harmonic vibration during the portion of time thatitis vibrating freely, in order to introduce high order undulations which cause the reed to ripple or rock across the indicia, as seen in FIGS. 9D

through 9l, one or more times before the electromagnet 44 is again energized, FIG. 91. For this purpose, a portion of reed 36 desirably contacts core 42 during the energization of the electromagnet. Such action introduces a secondary resonance into the primary or fundamental resonance of the reed, producing the desired high harmonic content. More particularly, referring to FIG. 9A, it will be noted that each reed 36 has a primary or fundamental resonance which is that of a freely vibratable reed clamped at one end, namely clamped at 38. As the reed is drawn downwardly, it desirably strikes end 41b, introducing a secondary resonance which is that of a freely vibratable reed clamped at one end and supported on a fulcrum at the other end, namely clampedat 38 and supported at 42b. As electromagnet 44 now releases reed 36 for free vibration, it exhibits both primary and first order harmonic oscillation.

' With this invention an improved printing action is attained to insure good image transfer, especially with the use of chemically treated paper such as the aforementioned Action Paper. The printing wheels which carry the raised indicium thereon are preferably molded in plastic with the raised indicium following a generally circular outline. Such printing wheels are cheaper to manufacture, and also lessen the drag of the paper on the wheels, thus reducing the power requirements of the servomechanism, but in the past have presented problems in obtaining good image transfer. As a result of the repeated rocking or massaging action obtained vibrating the reeds, such circular printing wheels can be utilized and high quality printing transfer is obtained. The lost motion connection interposed in the servomechanism drive train and the index means afforded by the electromagnet and adjacent toothed wheel on the printing drive shaft insure that the variable value print wheels will be oriented in a proper printing position responsive to each input signal received by the servomechanism. In cooperation with this, the individual reed elements will engage only each individual 'p'rint' wheel avoiding problems of bridging" with the result that a sharply defined print transfer will be obtained.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitation should be understood therefrom, as some modifications will be obvious to those skilled in the art.

We claim:

1. A printing station, comprising:

a character image member'having a raised character occupying a first extent;

vibratable means spaced from said character-image member and formed of flexible material;

a sheet between said member and said vibratable means;

and

means for exciting said vibratable means to cause a ripple movement therein which urges saidsheet and said vibratable means against less than said first extent of said raised character, said ripple movement repeatedly rocking said sheet and said vibratable means across said first extent to transfer the complete character image of said member to said sheet. I

2. The printing station of claim 1 wherein said vibratable means comprises a thin elongated reed having dimensions to allow undulations therein which transversely displace the 3. The printing station of claim 2 including means to introduce a harmonic oscillation in said reed when vibrating in said natural mode of oscillation, said harmonic oscillation causing said reed to repeatedly rock across said first extent.

4. The printing station of claim 2 wherein said exciting means causes said reed to vibrate through a cycle of undulations, and means for actuating said exciting means a plurality of times to cause said reed to repeatedly rock across said member to enhance the transfer of the character image to the sheet.

5. The printing station of claim 2 wherein said reed has a natural frequency of vibration for said natural mode of oscillation, and said exciting means is enabled generally in synchronism with the natural frequency of vibration of said reed in order that each excitation of said reed reinforces the undulations in said reed.

6. A printing station, comprising:

an impression carrier member having a character with an image to be transferred;

an elongated striking means closely spaced from said impression member to form a gap therebetween and having dimensions to allow undulations therein which transversely displace the elongated striking means through said a sheet located in said gap between said impression member and said striking means; and

means for exciting said striking means to cause multiple undulations in which the striking means repeatedly urges the sheet against said impression member to transfer a single 1 character image to the sheet.

7. The printing station of claim 6 wherein the striking means is a thin, elongate reed.

8. The printing station of claim 7 wherein the reed is formed of a material capable of being deflected by a magnetic field and wherein the exciting means is an electromagnet.

9. The printing station of claim 6 wherein the impression member is a rotatably displaceable print wheel with a plurality of characters formed in raised relief on the periphery of the wheel.

10. The printing station of claim 9 wherein the characters on the print wheel are arcuate segments generally following the periphery of the wheel. The striking means being a thin, elongate reed with a downturned extreme free end, vibration of the reed causing the reed to repeatedly urge the sheet against different areas of a single arcuate segment forming one character in order to transfer the entire image of the character to the sheet.

' 11. The printing station of claim 9 wherein a plurality of print wheels are mounted on a rotatable shaft with an elongated striking means adjacent each print wheel.

12. The printing station of claim 11 including energizable clamping means for urging the plurality of print wheels against each other, and means for energizing said clamping means during the time of character image transfer.

13. The printing station of claim 11 wherein said striking means comprises a unitary metal plate having a plurality of extending elongated fingers, each finger being adjacent a different one of said plurality of print wheels, and means clamping said plate to allow each finger to act as an independent cantilevered reed.

14. A printing station for impressing an image on a sheet, comprising:

a movable print carrier having a plurality of characters formed in raised relief;

means for moving said carrier to locate individual ones of said characters at a print position;

a flexible elongated striker formed of metallic material;

cantilever means for clamping said striker to form a cantilever free portion located adjacent said print position, said flexible striker being excitable to cause undulations which transversely displace the cantilever free portion in the vicinity of said print position;

feed means locating said sheet between said cantilevered free portion of said striker and said individual one image which is to be transferred Esaid sheet, and means for causing said cantilevered free portion of said striker to repeatedly urge said sheet against different areas which in sum form said arcuate planar surface, whereby the entire image is transferred to said sheet.

16. The printing station of claim 14 wherein the cantilevered free portion of said striker has dimensions which fix a natural resonant frequency of vibration tuned below the frequency of energization of said electromagnet means. 

